This invention relates to a vertical engine for a walk-behind lawn mower and more particularly to an improved construction for air cooling an engine having its output shaft rotatable about a vertically extending axis.
Air-cooled engines find a wide variety of applications. One of the large volume applications for such engines is in powering certain implements such as walk-behind rotary lawn mowers. With such applications, the engine is normally positioned with the cylinder extending in a horizontal direction and with the output shaft rotating about a vertically extending axis. This has particular utility because it permits the engine output shaft to be directly coupled to the cutting blade, which rotates about a vertically extending axis, and thus affords a simple construction. However, there are a wide variety of difficulties in connection with the air cooling of an engine having such an orientation.
Specifically, one of the problems in cooling an engine of this configuration is that the air flow generally flows in a downward direction over the engine and specifically the cylinder barrel for its cooling. However, the immediately adjacent configuration of the lawn mower housing tends to obstruct such flow and may, in fact, redirect it so that the hot gases are directed across a portion of the engine which should be cooled or at least not heated. For example, it is very desirable to maintain the carburetor of the engine at a relatively low temperature so as to improve the induction efficiency and to preclude the evaporation of fuel from the heat of the engine.
It is, therefore, a principle object of this invention to provide an improved arrangement for air cooling the engine of a rotary lawn mower.
It is a further object of this invention to provide an improved layout for an engine and rotary lawn mower wherein the carburetor of the engine would not be unduly heated.
In addition to the problem of cooling the carburetor and preventing undue heating of it, it is also desirable to maintain the carburetor in relatively close proximity to the combustion chamber. Since the combustion chamber is one of the hottest portions of the engine, there is a tendency to attempt to position the carburetor at a remote distance from the cylinder head and combustion chamber so as to avoid the aforenoted heat problems. However, as the runner passage from the carburetor to the combustion chamber increases in length, starting, particularly at low temperatures, becomes difficult.
It is, therefore, a still further object of this invention to provide an improved arrangement for an engine wherein the carburetor may be positioned close to the combustion chamber.
It is a further object of this invention to provide an engine configuration wherein the carburetor will be cooled but nevertheless is in close proximity to the combustion chamber.
Utility engines employed for driving implements such as rotary lawn mowers have frequently used very simple engines having L-head construction. Although the simplicity of such engines have a number of advantages, the performance of these engines are considerably reduced from those of overhead valve engines. However, if a small overhead valve engine is employed and is utilized in conjunction with an implement such as a rotary lawn mower, certain difficulties arise in connection with the air cooling of the engine. For example, the positioning of the various components such as the exhaust manifold, muffler and air cleaner can, as aforenoted, present certain difficulties. It is, therefore, a further object of this invention to provide an improved air-cooling arrangement for the intake and exhaust valves of an air-cooled engine.
It is a further object of this invention to provide an improved air-cooling arrangement for an air-cooled overhead valve engine that operates with the cylinder disposed in a horizontal orientation.
Regarding the cooling of overhead valve internal combustion engines by air systems, it is normally the practice to operate valves by means of rocker arms that are pivotally supported within the cylinder head and are operated by means of push rods. However, it is important to ensure that the valve operating components are also adequately cooled.
It is yet a further object of this invention to provide an improved air-cooling arrangement for the push rods and valve actuators of an engine.